A polycarbonate resin is excellent in mechanical strength (especially, impact resistance), electrical properties, transparency, etc., and has been widely used as an engineering plastic in various fields such as office automation (hereinafter referred to as OA) equipment, electrical and electronic equipment, automobiles, etc. Among them, there is a field in which flame retardancy is required, mainly in the fields of OA equipment, and electrical and electronic equipment. A polycarbonate resin has a high oxygen index among various thermoplastic resins, and is generally considered to be a resin with self-extinguishing properties. However, the flame retardancy level required in the fields of OA equipment and electrical and electronic equipment is generally so high as the V-0 level of UL 94 Standards on flame retardancy, that other flame retardants and auxiliaries are usually added in order to impart the flame retardancy meeting the level.
On the other hand, it is known that a polycarbonate-polyorganosiloxane copolymer or a mixture of the polycarbonate-polyorganosiloxane copolymer and a polycarbonate resin generally shows higher flame retardancy than that of the polycarbonate resin. However, since the flame retardancy of the polycarbonate-polyorganosiloxane copolymer alone is not sufficient to meet the above-mentioned level of the flame retardancy, a composition in combination with various flame retardants has been disclosed (for example, Japanese Patent Application Laid-Open No. 289059/1988 (Showa 63), Japanese Patent Application Laid-Open No. 210462/1989 (Heisei 1), Japanese Patent Application Laid-Open No. 200862/1991 (Heisei 3), Japanese Patent Application Laid-Open No. 202465/1992 (Heisei 4), Japanese Patent Application Laid-Open No. 320519/1993 (Heisei 5), Japanese Patent Application Laid-Open No. 36836/1994 (Heisei 6), Japanese Patent No. 3007046, etc.). However, these disclosed techniques have a drawback, wherein thermal stability is in general decreased when a bromine compound is added as a flame retardant. In the case when a phosphorus compound is added, fluidity is improved, while heat resistance decreases. Especially, when environmental problems are taken into consideration, it has been considered generally difficult to achieve flame retardancy and high reflectance at the same time in a thin-walled molding with a wall thickness of 1 mm or less for a product required in a reflecting plate and the like used for backlight of a liquid crystal display etc., without using a bromine compound or a phosphorus compound.
Furthermore, when such a polycarbonate resin composition is formed to an extruded sheet molding, since not only high reflectance but also high light-shutting properties are required for optical properties in light reflecting applications such as a backlight reflecting plate etc. of a liquid crystal display etc., it is necessary to blend titanium oxide in a high concentration. However, when the titanium oxide was blended in a high concentration, there was a problem in that a polycarbonate resin matrix became degraded, and consequently the light reflectance of a resin molding decreased. Also, when the titanium oxide is blended in a large quantity, decrease in the molecular weight of the polycarbonate becomes substantial, which causes reduction in the mechanical strength. A polycarbonate resin composition blended with titanium oxide, having a good mechanical strength and excellent optical properties after improving the above-mentioned problems has been disclosed in Japanese Patent Application Laid-Open No. 320519/1993 (Heisei 5). Nevertheless, a polycarbonate resin composition is desired, which, in addition to further improving these properties, exhibits excellent flame retardancy without adding a phosphorus compound flame retardant or a halogenated flame retardant while maintaining heat resistance, and also satisfies high reflectance and high light-shutting properties in terms of optical properties.